Bug Fables: The Everlasting Sapling

For this achievement you have to use the spy in battle on every enemy in the game. Once you spy on an enemy it'll show their health below them in all future battles. I used that as an indicator on which enemies I have added to the bestiary. You can use the spy specs medal(obtained by defeating 3 mini bosses or 6 bosses in boss rush mode at the B.O.S.S machine in hive kingdom) as it won't use up a turn when you spy and it will also show the health of each enemy regardless if you have it in your bestiary. I didn't use it since it's harder to tell which ones you haven't spied on yet.

Don't worry if you miss a few enemies, you can use berries to fill in what you missed from a bug in the Underground Tavern as long as you have encountered them at least once in battle. It's 19 berries for regular enemies and 49 for bosses/mini bosses. So as long as you keep enough berries in the bank by the end of the game you should have accrued enough interest to buy out the entire bestiary. But it would be wiser to save those berries for the cooking maestro achievement.

Below I will list each enemy in order as shown in the bestiary along with where you can find them.

1: Seedling
Locations: Bugaria Outskirts, Golden Path, Golden Hills, Snakemouth Den

2: Acornling
Locations: Golden Path, Golden Hills, Sacred Hills

3: Underling
Locations: Bugaria Outskirts, Lost Sands

4: Cactiling
Locations: Lost Sands

5: Flowerling
Locations: Far Grasslands, Wild Swamplands

6: Plumpling
Locations: Forsaken Lands

7: Golden Seedling
Locations: You can find these in the same locations as the Seedling but you'll have a better chance in Seedling Haven, located across the river on the way to Snakemouth Den. In normal areas there is a 1% chance you'll encounter them or 2.5% with the Seedling affinity medal(obtained by completing the Seedling hunt quest) In Seedling Haven there's a 7.5% chance or 18.75% with the Seedling Affinity medal

8: Zombiant
Locations: Snakemouth Den, Upper Snakemouth

9: Zombee
Locations: Upper Snakemouth

10: Zombeetle
Locations: Upper Snakemouth

11: Jellyshroom
Locations: Snakemouth Den, Upper Snakemouth

12: Bloatshroom
Locations: Upper Snakemouth

13: Inichas
Locations: Snakemouth Den

14: Denmuki
Locations: Honey Factory

15: Madesphy
Locations: Wild Swamplands

16: Numbnail
Locations: Golden Path, Golden Hills, Golden Cave

17: Ironnail
Locations: Forsaken Lands, Golden Cave

18: Midge
Locations: Golden Cave, Golden Path, Golden Hills, Lost Sands, Bugaria Outskirts

19: Chomber
Locations: Golden Path, Golden Hills, Sacred Hills, Lost Sands, Chomper Cave

20: Chomper Brute
Locations: Chomper Cave

21: Wild Chomper
Locations: Far Grasslands, Wild Swamplands

22: Weevil
Locations: Golden Path, Golden Hills

23: Psicorp
Locations: Lost Sands, Ancient Castle

24: Arrow Worm
Locations: Lost Sands, Ancient Castle

25: Thief
Locations: Lost Sands, Bandit Hideout

26: Bandit
Locations: Lost Sands, Bandit Hideout

27: Burglar
Locations: Lost Sands, Bandit Hideout

28: Ruffian
Locations: Rubber Prison

29: Bee-Boop
Locations: Honey Factory

30: Security Turret
Locations: Honey Factory

31: Mender
Locations: Honey Factory

32: Abomihoney
Locations: Honey Factory

33: Ahoneynation
Locations: Honey Factory

34: Krawler
Locations: Ancient Castle, The Fridge, Giant's Lair

35: Warden
Locations: Ancient Castle, The Fridge, Giant's Lair

36: Haunted Cloth
Locations: Ancient Castle, Giant's Lair

37: Leafbug Ninja
Locations: Wild Swamplands

38: Leafbug Archer
Locations: Wild Swamplands

39: Leafbug Clubber
Locations: Wild Swamplands

40: Mantidfly
Locations: Far Grasslands, Wild Swamplands

41: Jumping Spider
Locations: Far Grasslands, Wild Swamplands

42: Mimic Spider
Locations: Forsaken Lands

43: Diving Spider
Locations: Metal Lake, Stream Mountain

44: Water Strider
Locations: Metal Lake, Stream Mountain

45: Belostoss
Locations: Golden Cave, Stream Mountain

46: Mothfly
Locations: Forsaken Lands

47: Mothfly Cluster
Locations: Forsaken Lands

48: Wasp Scout
Locations: Wasp Kingdom Hive, Rubber Prison, Metal Lake

49: Wasp Trooper
Locations: Bugaria Outskirts, Wasp Kingdom Hive, Metal Lake, Rubber Prison

50: Wasp Bomber
Locations: Wasp Kingdom Hive, Rubber Prison

51: Wasp Driller
Locations: Wasp Kingdom Hive, Rubber Prison

52: Venus' Bud
Locations: Golden Settlement, Golden Hills, Sacred Hills

53: Acolyte Aria
Locations: Golden Settlement

54: Mothiva
Locations: Golden Hills, Termite Colosseum

55: Zasp
Locations: Golden Hills, Termite Colosseum

56: Astotheles
Locations: Bandit Hideout

57: Dune Scorpion
Locations: Lost Sands

58: Primal Weevil
Locations: Forsaken Lands, Termite Capitol

59: Cross
Locations: Termite Capitol

60: Poi
Locations: Termite Capitol

61: Spider
Locations: Snakemouth Den

62: Venus' Guardian
Locations: Sacred Hills

63: Heavy Drone B-33
Locations: Honey Factory

64: The Watcher
Locations: Ancient Castle

65: The Beast
Locations: Wild Swamplands

66: General Ultimax
Locations: Wasp Kingdom Hive, Rubber Prison

67: Ultimax Tank
Locations: Rubber Prison

68: Mother Chomper
Locations: Chomper Cave (East 1 room from Golden Settlement then drop down, Cave is to the left)

69: Broodmother
Locations: Power Plant (West of Golden Settlement)

70: Zommoth
Locations: Upper Snakemouth (Lief's request quest)

71: Seedling King
Locations: Seedling Haven (West 1 room from Ant Kingdom then immediately cross the river)

72: Tidal Wyrm
Locations: Stream Mountain (where you Lower the water drop down and it's west a couple rooms)

73: Peacock Spider
Locations: Peacock Island (Southeast from Metal Island)

74: Devourer
Locations: Golden Path (North a few rooms of the rising platform using Vi's beemerang)

75: False Monarch
Locations: Ancient City in Forsaken Lands (2 rooms West of the pipes with air currents)

76: Cenn
Locations: Bugaria Outskirts (Explorer Check! quest)

77: Pisci
Locations: Bugaria Outskirts (Explorer Check! quest)

78: Monsieur Scarlet
Locations: Golden Cave (Requesting Assistance quest)

79: Kabbu
Locations: Defiant Root (Stolen Item quest)

80: Kali
Locations: Defiant Root (Stolen Item quest)

81: Carmina
Locations: Metal Island (gain access of inn by doing card masters of Bugaria quest)

82: Riz
Locations: Far Grasslands

83: Maki
Locations: Ant Kingdom City (confidential quest)

84: Kina
Locations: Ant Kingdom City (Confidential quest)

85: Yin
Locations: Ant Kingdom City (Confidential quest)

86: Stratos
Locations: Underground Tavern (Getting Bored quest)

87: Delilah
Locations: Underground Tavern (Getting Bored quest)

88: Dead Lander α
Locations: Giant's Lair

89: Dead Lander β
Locations: Giant's Lair

90: Dead Lander γ
Locations: Giant's Lair

91: Wasp King
Locations: Giant's Lair

92: The Everlasting King
Locations: Giant's Lair

With your now filled bestiary, go beat everyone in Bugaria at spy cards!